Although ejection of a seat and its occupant from an aircraft is a life-preserving technique which has been known and used for many years, it is still and will remain a somewhat hazardous event because of the inescapable facts that the aircraft from which the occupant is being ejected is usually traveling at a rather high speed and the seat is not designed to be an efficient "flying machine". Although structures have been proposed to enclose the pilot in a capsule of some sort as he is separated from the aircraft, most such proposals are not feasible for most aircraft because they add greatly to the aircraft weight, require substantial modifications to aircraft design and excessively complicate arranging the controls used by the pilot during normal flight.
The most effective and acceptable system thus uses the seat itself to carry the pilot (or other occupant) out of the aircraft after which the pilot or, in some systems the seat and pilot, are lowered by parachute to safety. Such systems have become quite reliable and greatly enhance the safe survival chances of an occupant who finds himself in an aircraft no longer able to fly, but they still subject the occupant to physiological stresses and, because of the erratic movement of the seat after it has been suddenly introduced into the airstream outside of the aircraft, can also put undesirable strains on the equipment.